fix CR suggestion and add tests

Author: Picazsoo

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringPageableScanUtils.java

@@ -164,7 +164,7 @@ public static Map<String, List<String>> scanSortValidationEnums(
                     Schema<?> enumSchema = schema;
                     if (ModelUtils.isArraySchema(schema)) {
                         enumSchema = schema.getItems();
-                        if (enumSchema.get$ref() != null) {
+                        if (enumSchema != null && enumSchema.get$ref() != null) {
                             enumSchema = ModelUtils.getReferencedSchema(openAPI, enumSchema);
                         }
                     }

modules/openapi-generator/src/test/java/org/openapitools/codegen/languages/SpringPageableScanUtilsTest.java

@@ -0,0 +1,154 @@
+package org.openapitools.codegen.languages;
+
+import io.swagger.v3.oas.models.OpenAPI;
+import io.swagger.v3.oas.models.Operation;
+import io.swagger.v3.oas.models.PathItem;
+import io.swagger.v3.oas.models.Paths;
+import io.swagger.v3.oas.models.media.ArraySchema;
+import io.swagger.v3.oas.models.media.Schema;
+import io.swagger.v3.oas.models.media.StringSchema;
+import io.swagger.v3.oas.models.parameters.Parameter;
+import org.testng.annotations.Test;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+
+/**
+ * Unit tests for {@link SpringPageableScanUtils}.
+ */
+public class SpringPageableScanUtilsTest {
+
+    // -------------------------------------------------------------------------
+    // Helpers
+    // -------------------------------------------------------------------------
+
+    /**
+     * Builds an OpenAPI doc with a single GET /items operation marked x-spring-paginated.
+     */
+    private static OpenAPI buildPageableOperation(Parameter sortParam) {
+        Operation op = new Operation();
+        op.setOperationId("listItems");
+        op.addExtension("x-spring-paginated", true);
+        op.addParametersItem(sortParam);
+
+        PathItem pathItem = new PathItem();
+        pathItem.setGet(op);
+
+        Paths paths = new Paths();
+        paths.addPathItem("/items", pathItem);
+
+        OpenAPI openAPI = new OpenAPI();
+        openAPI.setPaths(paths);
+        return openAPI;
+    }
+
+    // -------------------------------------------------------------------------
+    // scanSortValidationEnums — NPE regression for array schema without items
+    // -------------------------------------------------------------------------
+
+    /**
+     * Regression: array sort parameter with no {@code items} must not throw NPE.
+     * {@code isArraySchema()} returns {@code true} but {@code schema.getItems()} returns
+     * {@code null}, which would NPE on the subsequent {@code enumSchema.get$ref()} call
+     * before the fix.
+     *
+     * <pre>
+     * parameters:
+     *   - name: sort
+     *     in: query
+     *     schema:
+     *       type: array
+     *       # items: intentionally absent
+     * </pre>
+     */
+    @Test
+    public void scanSortValidationEnums_arraySchemaWithNoItems_doesNotThrow_and_returnsEmptyMap() {
+        // sort param: type=array but items intentionally absent
+        Schema<?> sortSchema = new ArraySchema();
+        // getItems() == null
+        assertThat(sortSchema.getItems()).isNull();
+        Parameter sortParam = new Parameter().name("sort").schema(sortSchema);
+        OpenAPI openAPI = buildPageableOperation(sortParam);
+
+        // does not throw NPE
+        assertThatCode(() -> SpringPageableScanUtils.scanSortValidationEnums(openAPI, false))
+                .doesNotThrowAnyException();
+
+        // and returns empty map
+        Map<String, List<String>> result = SpringPageableScanUtils.scanSortValidationEnums(openAPI, false);
+        assertThat(result).isEmpty();
+    }
+
+    // -------------------------------------------------------------------------
+    // scanSortValidationEnums — happy path
+    // -------------------------------------------------------------------------
+
+    /**
+     * <pre>
+     * parameters:
+     *   - name: sort
+     *     in: query
+     *     schema:
+     *       type: array # sort as multi-column
+     *       items:
+     *         type: string
+     *         enum: ["name,asc", "name,desc", "id,asc"]
+     * </pre>
+     */
+    @Test
+    public void scanSortValidationEnums_arraySchemaWithEnumItems_returnsMappedEnums() {
+        Schema<?> items = new StringSchema()._enum(List.of("name,asc", "name,desc", "id,asc"));
+        Schema<?> sortSchema = new ArraySchema().items(items);
+        Parameter sortParam = new Parameter().name("sort").schema(sortSchema);
+        OpenAPI openAPI = buildPageableOperation(sortParam);
+
+        Map<String, List<String>> result = SpringPageableScanUtils.scanSortValidationEnums(openAPI, false);
+        assertThat(result)
+                .containsKey("listItems")
+                .satisfies(m -> assertThat(m.get("listItems"))
+                        .containsExactly("name,asc", "name,desc", "id,asc"));
+    }
+
+    /**
+     * <pre>
+     * parameters:
+     *   - name: sort
+     *     in: query
+     *     schema:
+     *       type: string # sort as single-column
+     *       enum: ["id,asc", "id,desc"]
+     * </pre>
+     */
+    @Test
+    public void scanSortValidationEnums_nonArraySortSchemaWithEnum_returnsIt() {
+        Schema<?> sortSchema = new StringSchema()._enum(List.of("id,asc", "id,desc"));
+        Parameter sortParam = new Parameter().name("sort").schema(sortSchema);
+        OpenAPI openAPI = buildPageableOperation(sortParam);
+
+        Map<String, List<String>> result = SpringPageableScanUtils.scanSortValidationEnums(openAPI, false);
+        assertThat(result)
+                .containsKey("listItems")
+                .satisfies(m -> assertThat(m.get("listItems")).containsExactly("id,asc", "id,desc"));
+    }
+
+    /**
+     * <pre>
+     * parameters:
+     *   - name: sort
+     *     in: query
+     *     schema:
+     *       type: string # sort as single-column
+     *       # enum: absent — no validation constraint
+     * </pre>
+     */
+    @Test
+    public void scanSortValidationEnums_sortSchemaWithNoEnum_returnsEmptyMap() {
+        Parameter sortParam = new Parameter().name("sort").schema(new StringSchema());
+        OpenAPI openAPI = buildPageableOperation(sortParam);
+
+        assertThat(SpringPageableScanUtils.scanSortValidationEnums(openAPI, false)).isEmpty();
+    }
+}